That year he formed the firm of Trost & Trost with his brother Gustavus Adolphus Trost, an architect. Adolphus Gustavus Trost was Gustavus' twin brother; in 1908 he joined the firm as a structural engineer.

Between 1903 and Henry Trost's death on September 19, 1933, the firm designed hundreds of buildings in the El Paso area and in other Southwestern cities, including Albuquerque, Phoenix, Tucson, and San Angelo.

Many of the buildings designed by Trost & Trost display an influence from the Chicago School of architecture.Henry Trost had lived in Chicago between 1888 and 1896. In 1889, Henry started the American Art Metal Work Company with Emil Henry Seeman which lasted about 1 year. It is from 1892 to 1896, that Trost served as vice president of Chicago Ornamental Iron Company. The company is associated with metal ornament that formed the front railings of the boxes and balconies in the Lafayette Square Opera House in Washington, D.C.